The present invention relates to the apparatuses and method of wavelength tunable laser with wavelength locker and power monitor. More particularly, this invention relates to a laser resonant cavity implemented with wavelength shift compensated acousto-optic tunable filter and wavelength locker and power monitor design by which the fast tuning speed, stable wavelength and power performance can be realized.
Most modern telecommunications systems are based on fiber optic transmission. The fiber optic networks offer both unprecedented capacity and the deployment flexibility needed to support a wide range of evolving and emerging broadband applications. Widely tunable lasers help to maximize existing fiber optic network resource. The ability to dynamically provision bandwidth provides the ability to move traffic from overcrowded channels to unused channels to meet the demands for Internet access. Tunable laser is also a key prerequisite as networks move towards full mesh-based optical networks where light paths can be set up and changed quickly and easily.
The main features of an ideal tunable laser for such applications can be summarized as follows: wide tuning range covering C and/or L band (about 1530 nanometers to about 1610 nanometers), small footprint, fast tuning speed (in submilliseconds) between any two International Telecommunication (ITU) grids, long term performance stability (over 25 years of operation), highly reliable under severe work conditions, low electrical power consumption, low cost and high manufacturability.
Tunable lasers, especially compact, wide tuning range and high power output tunable lasers, have many applications in biology, medical instrumentation, fiber optic sensor network, etc.
Unfortunately, market penetration of tunable lasers is inhibited by the limitations of existing tunable lasers in their compactness, wavelength tuning range, tuning speed and output power, etc. The current tunable laser systems can be classified into the three types, systems use mechanically movable intracavity elements such as diffraction gratings, prisms, etalons or MEMS (Microelectromechanical systems) as the wavelength tuning elements; systems with thermally tunable elements built into the cavity and wavelengths are selected through thermally heating or cooling the elements; systems employ non-movable intracavity optical elements for tuning, which involves the use of Magneto-optic, Acousto-optic, Electro-optic elements or electric current injection to physically select the wavelength.
Tuning techniques that rely on mechanical adjustment of the angle of a grating or prism, is very susceptible to the mechanical shock and vibration causing short term and long term performance instability, therefore tunable lasers employing moving parts are not suitable for optical telecom applications. Thermal tuning is intrinsically slow, and therefore its applications are limited. Among the technologies which are based on tuning wavelength physically, acousto-optic technology which has been used as tuning element due to its electronic tunability without moving part, fast tuning speed, wide tuning ranges and simplicity to implement, is a viable approach to meet the stringent requirements of tunable lasers for telecom applications as described above. By appropriately selecting the acousto-optical crystals and driving acoustic frequencies, a tunable laser can be designed for operation within a wide range of wavelength spectrum, and for different applications as has been disclosed in some U.S. patents. The key problems with the existing design of external cavity tunable laser utilizing acousto-optic filter for application in fiber optic telecom network are: (1) Doppler frequency shift compensation is usually achieved by two crystals, which makes alignment very difficult. (2) two RF transducers bonded on the same crystal as disclosed in some US patens, which significantly increases the cost. The present invention addresses these issues.